Urbanisation in Asia blamed for lethal epidemic of dengue fever

Dengue fever is sweeping south-east Asia in an outbreak of the mosquito-borne virus that is already threatening to become the worst in almost a decade.

Hospitals across the region are filling up and the number of deaths mounting with no country left immune, from the richest, ultra-modern Singapore, to the poorest, such as Laos and Cambodia. The number of cases in many countries is already well above the total for 2006 and is on course to match 1998 - the worst year on record, when 1,500 died out of 350,000 infected.

In a worrying harbinger of the future, globalisation and rising prosperity in Asia's huge cities are cited as key reasons for dengue's growing prevalence. The Aedes aegypti mosquito that carries dengue - known as the "bone-breaker" illness because of its joint pain - multiplies in clean water, with every pool, discarded plastic bag or tin can a potential breeding ground during the rainy season.

The migration of workers in the region and rapid urbanisation are other factors.

Singapore's building sites, full of migrant workers, have been the focus of outbreaks as mosquitoes bite infected workers and then pass the disease to others. But Aedes mosquitoes have also been found on the 50th floors of the city-state's gleaming glass and steel skyscrapers.

Yet poor countries are hit hardest. World Health Organisation (WHO) figures reveal that Cambodia has suffered 25,000 cases this year, killing 300 children under 15 - three times the number for all of 2005.

Across Indonesia, more than 100,000 dengue cases have been recorded, killing 1,100. Health officials in Jakarta believe the number will hit 200,000 by the year's end, compared with 114,000 in 2006.

Malaysia has also seen a 50% leap in infections, with 56 deaths recorded in June and more than 1,000 patients admitted to hospital every week in July.

Vietnam, which invariably experiences large numbers of dengue cases, has seen a 40% jump on last year. This year 33,000 people were infected, with 32 deaths.

Aedes mosquitoes bite only in daytime, unlike malaria-carrying mosquitoes. Often those infected with dengue suffer a mild form with flu-like symptoms and may not realise they have the disease. Aside from joint pain, dengue victims experience rashes, nausea and headaches. But some also suffer a potentially fatal form called dengue haemorrhagic fever, which causes internal bleeding and circulatory failure.

No vaccine has yet been found for any of the four strains of dengue virus, none of which confer immunity from the others.

Dr Chusak Prasittisuk, a WHO south-east Asian communicable diseases coordinator, said: "In expanding cities water supplies are insufficient, so people use containers that become breeding grounds. This is a man-made problem."

Health experts fear that this year's spike in dengue cases could become the norm. Dr Axel Kroeger, a WHO dengue research coordinator in Geneva, said: "We always think next year it will get better but we always find next year it gets worse. There's a very clear upward trend."